Capturing groups and backreferences in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to match a word using a capturing group.

PHP

<?php
$pattern = '/(\w+)[1]/';
$text = 'Hello';
if (preg_match($pattern, $text, $matches)) {
    echo $matches[1];
}
?>

Drag options to blanks, or click blank then click option'

A+

B*

C?

D{2}

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*' matches zero or more, which might match empty strings.

Using '?' matches zero or one, which might not capture the full word.

The + quantifier matches one or more of the preceding token, so (\w)+ captures one or more word characters.

2fill in blank

medium

Complete the code to use a backreference to match repeated words.

PHP

<?php
$pattern = '/(\w+)[1]\1/';
$text = 'hello hello';
if (preg_match($pattern, $text)) {
    echo 'Match found';
}
?>

Drag options to blanks, or click blank then click option'

A\d+

B\S+

C\w+

D\s+

Attempts:

3 left

💡 Hint

Common Mistakes

Using \d+ matches digits, not spaces.

Using \w+ matches word characters, which won't match spaces.

The backreference \1 matches the same text as the first capturing group. The \s+ matches one or more whitespace characters between the repeated words.

3fill in blank

hard

Fix the error in the pattern to correctly match a repeated word using backreference.

PHP

<?php
$pattern = '/(\w+)[1]\1/';
$text = 'test test';
if (preg_match($pattern, $text)) {
    echo 'Repeated word found';
}
?>

Drag options to blanks, or click blank then click option'

A\d+

B\w+

C\s+

D\S+

Attempts:

3 left

💡 Hint

Common Mistakes

Using \w+ or \d+ which do not match spaces.

Not escaping the backslash properly.

The pattern needs to match whitespace between the repeated words. Using \s+ fixes the error.

4fill in blank

hard

Fill both blanks to create a pattern that matches a word repeated twice with a space between.

PHP

<?php
$pattern = '/([1])[2]\1/';
$text = 'echo echo';
if (preg_match($pattern, $text)) {
    echo 'Match!';
}
?>

Drag options to blanks, or click blank then click option'

A\\w+

B\\d+

C\\s+

D\\S+

Attempts:

3 left

💡 Hint

Common Mistakes

Using \d+ for the word, which matches digits only.

Using \S+ for the space, which matches non-space characters.

The first blank should capture one or more word characters (\w+), and the second blank should match one or more whitespace characters (\s+) between the repeated words.

5fill in blank

hard

Fill all three blanks to create a pattern that matches a repeated word separated by a comma and space.

PHP

<?php
$pattern = '/([1])[2]\1[3]/';
$text = 'word, word ';
if (preg_match($pattern, $text)) {
    echo 'Pattern matched';
}
?>

Drag options to blanks, or click blank then click option'

A\\w+

B\\s*,\\s*

C\\s+

D,

Attempts:

3 left

💡 Hint

Common Mistakes

Using a literal ', ' for the comma and space, which is less flexible.

Not matching spaces properly around the comma.

The first blank captures one or more word characters (\w+). The second blank matches a comma possibly surrounded by spaces (\s*,\s*). The third blank matches one or more spaces (\s+) after the repeated word.